The goals of this project are to determine the role of I-region associated (Ia) antigens in the regulation of immunocompetent cell interactions and to determine the mechanism of action and site of expression of the major histocompatibility linked immune response (Ir) genes. We have analyzed the immune responses of guinea pig T lymphocytes which have been primed in vitro with allogeneic bovine insulin pulsed macrophages and have demonstrated that strain 2 macrophages were fully competent to present bovine insulin B chain to strain 13 T cells despite the fact that strain 2 guinea pigs are normally totally unresponsive to this antigen. In addition, a comparison of the reactivity profiles of self-Ia- and allo-Ia-restricted strain 13 T cells to a series of synthetic B chain peptide fragments revealed that the allo-Ia restricted populations could be activated by guinea pig insulin. These observations suggest that the clonal deletion of self-reactive cells is likely to be I-region restricted and that nonresponsiveness to any protein antigen may result from a restriction in the T cell repertoire that is generated during ontogeny by a clonal deletion mechanism of tolerance to self. In a related series of studies, we have analyzed the fate of soluble protein antigens following pulse exposure of antigen-presenting macrophages. We have identified a critical, stable pool of antigen confined to the macrophage cell surface; no evidence was obtained to support the notion that a significant amount of antigen that was initially internalized after the pulse exposure was recompartmentalized to the cell surface. The combined use of these genetic and biochemical approaches has resulted in a model of macrophage antigen handling that only requires surface events to yield an immunogenic moiety to be displayed in the context of Ia antigens to primed T cells.